What started out as a fun night ended with an ugly morning for two actresses in Hollywood. On Friday, April 5, Jaime Pressly and Estella Warren joined several other stars at a birthday party in L.A. Everyone was having a great time -- until Pressly, 35, got into an argument with Warren, 34, at celebrity hotspot Bootsy Bellows. The confrontation escalated to the point that the police had to be called to intervene, and even then, it took hours to resolve the situation.

A source tells Us Weekly that things got "crazy" after Pressly and her assistant discovered that the assistant's purse had gone missing at the original party location, a house in L.A. Using one of those "find my phone" apps, the pair reportedly tracked the bag to Bootsy Bellows, where Warren and several other party guests (including Zac Efron and Adam Lambert) were continuing the celebration.

According to the source, Warren claimed the purse was hers, even though all of the assistant's things were still in it. "Jaime was trying to get it back," the insider tells Us. "She wasn't agressive, but she was forceful."

The two continued to fight, with Warren maintaining that she was the rightful owner, and Pressly insisting that the bag belonged to her assistant. At one point, the insider says, drugs were discovered in the purse, which led to the police getting involved. "Jaime and her assistant were volunteering for a drug test. They said the drugs weren't theirs," the eyewitness tells Us. "It was this crazy mess."

The West Hollywood Sheriff's Department confirms that they responded to two calls at Bootsy Bellows on April 5 -- a theft, at around 2 a.m., and a stolen vehicle -- but no other details were immediately available, as the investigation is still active.